Compositions and coatings with non-chrome corrosion inhibitor particles

ABSTRACT

Compositions are described for protecting a metal surface against corrosion. The composition includes a corrosion-inhibiting particle. The corrosion inhibiting particle may be usable in an epoxy resin-based coating or an olefin resin-based coating. The particle may include a core and a protectant. The core may include a water soluble corrosion inhibitor. The protectant may be disposed on at least a portion of a surface of the core and may be covalently or ionically bonded to a thiol group of the corrosion inhibitor. The protectant may be configured to reduce reaction between the core and the epoxy resin or the olefin resin.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 62/055,939, filed Sep. 26, 2014 the entirety of which isincorporated herein by reference.

FIELD

Disclosed herein are descriptions that relate generally to corrosioninhibiting particles, such as core-shell particles, and in particular tocorrosion-inhibiting particles that can be used in compositions andcoatings for corrosion control of metals.

BACKGROUND

Corrosion is defined as the chemical or electrochemical reaction betweena material, usually a metal, and its environment that produces adeterioration of the material and its properties. Corrosive attackbegins on the surface of the metal. The corrosion process involves twochemical changes. The metal that is attacked or oxidized undergoes ananodic change, with the corrosive agent being reduced and undergoing acathodic change. The tendency of most metals to corrode creates a majormaintenance challenge for metals and metal products, particularly inareas where adverse environmental or weather conditions exist.

Chromium-based anti-corrosive systems containing hexavalent chromiumcompounds have proven to be an extremely useful and versatile group ofchemistries that are extensively used in aircraft metal treatmentprocesses. They impart many beneficial anti-corrosive characteristics tometallic substrates on which they are applied and have been usedextensively for the pre-treatment of metals before coating, adhesivebonding and surface finishing. Chemically, chromium-based anti-corrosivesystems have involved the combination of hexavalent chromium (e.g.,CrO₃, CrO₄ ⁻², Cr₂O₇ ⁻²) and hydrofluoric acid (HF) in the case ofaluminum and its alloys. The hydrofluoric acid removes oxide film fromthe surface of the metallic substrate (e.g., aluminum) and thehexavalent chromium reacts with the exposed metal and a trivalentchromium oxide precipitates. Using aluminum as an example: Cr₂O₇⁻²+2Al⁰+2H⁺

Cr₂O₇.H₂O+Al₂O₃.

Chromium oxide, such as that produced according to the above reaction,is quite useful in anti-corrosive applications. It is quite stable inalkaline environments, it is water repellant (hydrophobic) and may actas a barrier coating towards water. Finally, it exhibits a “self-healingeffect”—that is, residual hexavalent chromium in the coating may reactwith damaged areas of the coating—thereby producing more trivalentchromium oxide at damaged sites and therefore “healing” itself.Consequently, chromium-based, and in particular hexavalentchromium-based systems have been extensively used in the aircraftindustry because they have proven to be: highly effective at reducingcorrosion and as an adhesion promoter for organic coatings andadhesives; particularly resilient as the application/treatment processexhibits a low sensitivity towards variation in process conditions;extremely effective on aluminum alloys; and ensure considerable qualitycontrol characteristics as a skilled worker may tell the amount ofchromium on the surface of a substrate by mere inspection (color) of thecoating.

Concern about chromium—and in particular, hexavalent chromium—in theenvironment has generated a need to replace chromium-based systems.Therefore “environmentally friendly”, commercially acceptablealternative to chromium-based systems are a welcome addition tocorrosion prevention coatings.

SUMMARY

Disclosed is a corrosion inhibiting particle. The corrosion inhibitingparticle may be usable in a sol gel coating for a pre-treatment orconversion coating alone or in combination with additional epoxy orolefin resin coating. The particle may include a core and a protectant.The core may include a water soluble corrosion inhibitor. The protectantmay be disposed on at least a portion of a surface of the core and maybe covalently or ionically bonded to a thiol group of the corrosioninhibitor. The protectant may be configured to reduce reaction betweenthe core and the epoxy resin or the olefin resin.

Also disclosed is a method for preparing a corrosion-inhibitingparticle. The method may include forming a core and forming a protectanton at least a portion of the core. The core may include a water solublecorrosion inhibitor. The protectant may be formed on at least a portionof the core by covalently or ionically bonding at least one of areactive component of a protectant-forming fluid to a thiol group of thecorrosion inhibitor.

Additionally, disclosed is an article that includes a metal substrateand a corrosion-inhibiting coating disposed on the substrate. Thecorrosion-inhibiting coating may include a corrosion-inhibitor particleincorporated in an epoxy and/or olefin or sol-gel based coating. Thecorrosion-inhibitor particle may include a core and a protectantdisposed on at least a portion of a surface of the core. The core mayinclude a corrosion inhibitor. The protectant may be covalently orionically bonded to a thiol group of the water solublecorrosion-inhibitor. The protectant may be configured to reduce reactionbetween the core and the epoxy or the olefin.

The particles, compositions and coatings disclosed herein may be usedfor providing corrosion protection and durability for articles such ascomponents of an airplane.

Additional advantages will be set forth in part in the description whichfollows, and in part will be understood from the description, or may belearned by practice thereof. The advantages will be realized andattained by means of the elements and combinations particularly pointedout in the appended claims.

It is to be understood that the foregoing general description and thefollowing detailed description are exemplary and explanatory and are notrestrictive of that which is claimed.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate examples and together with thedescription, serve to explain the principles of that which is describedherein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one example of an aircraft.

FIG. 2A illustrates an uncured coating composition that includes acorrosion inhibiting particle and at least one of an epoxy and/or olefinresin or sol-gel coating with the uncured coating composition disposedon a substrate.

FIG. 2B illustrates the coating formulation of FIG. 2A after curing onthe substrate.

FIG. 3 illustrates a corrosion inhibiting particle having a protectantdisposed on a surface of the corrosion inhibiting particle's core.

FIG. 4 is a flowchart depicting a method of making a corrosioninhibiting particle and corrosion inhibiting composition.

FIGS. 5A is an organic structure of a corrosion-inhibitor.

FIG. 5B illustrates a micronized core, the surface of which is enrichedwith mercaptan-terminated chains of a corrosion inhibitor.

FIG. 5C is an organic structure of an epoxy which may be used as aprotectant-forming composition, a matrix material of a coatingcomposition, or both.

FIG. 5D is a close-up view of a corrosion-inhibiting particle thatincludes a core and a protectant covalently bonded to thecorrosion-inhibitor of the core.

FIGS. 6A-6B includes microscope images of non-chromecorrosion-inhibiting particles. FIG. 6A shows larger, raw particles(i.e., before micronization), and FIG. 6B shows that the smaller,micronized particles resulting from the micronizing of the particles ofFIG. 6A.

FIGS. 7A-7C are images of 2024 T3 Aluminum test panels coated withvarious corrosion-inhibiting particles at 4% w/v in 6% v/v of reactantsin AC-131 (3M™ Surface Pre-Treatment AC-131). FIG. 7A shows a test panelcoated with a coating that comprises non-micronized INHIBICOR®1000particles. FIG. 7B shows a test panel coated with a coating thatcomprises micronized corrosion-inhibiting particles as described herein,and FIG. 7C shows a test panel coated with a coating that comprisesmicronized and neutralized particles according to the descriptionsprovided herein.

FIG. 8 is a Linear Sweep Voltammetry (LSV) graph showing effects ofmicronizing and neutralizing INHIBICOR® 1000 particles.

FIG. 9 is a chronoamperometry plot showing effects of micronizing andneutralizing INHIBICOR® 1000 particles.

DETAILED DESCRIPTION

Reference will now be made in detail to the present descriptions,examples of which are illustrated in the accompanying drawings. Whereverpossible, the same reference numbers will be used throughout thedrawings to refer to the same or like parts.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the descriptions are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value inherently contains certain errorsnecessarily resulting from the standard deviation found in theirrespective testing measurements. Moreover, all ranges disclosed hereinare to be understood to encompass sub-ranges subsumed therein. Forexample, a range of “less than 10” can include sub-ranges between (andincluding) the minimum value of zero and the maximum value of 10, thatis, any and all sub-ranges having a minimum value of equal to or greaterthan zero and a maximum value of equal to or less than 10, e.g., 1 to 5.In certain cases, the numerical values as stated for the parameter cantake on negative values. In this case, the example value of range statedas “less that 10” can assume negative values, e.g. −1, −2, −3, −10, −20,−30, etc.

The following is described for illustrative purposes with reference tothe Figures. Those of skill in the art will appreciate that thefollowing description is exemplary in nature, and that variousmodifications to the parameters set forth herein could be made withoutdeparting from the scope of the present disclosure. It is intended thatthe specification and examples be considered as examples. The variousdescriptions are not necessarily mutually exclusive, as somedescriptions can be combined with one or more other descriptions to formcombined descriptions.

Articles, such as metal surfaces that are subject to environmentalcorrosion, in particular to oxidative corrosion, such as those of anaircraft shown in FIG. 1, can be protected against such corrosion. Ametal surface of such an article may be protected by treating withcorrosion inhibiting particles, such as those included in acorrosion-inhibiting coating formed from a corrosion-inhibiting coatingcomposition. For example, as shown in FIGS. 2A-2B, acorrosion-inhibiting coating 109 can be formed on a surface of substrate103, which may be a metal, of article 100. An exemplary metal forsubstrate 103 comprises aluminum and aluminum alloys, steel, magnesiumand magnesium alloys, copper and copper alloys, tin and tin alloys,nickel alloys and titanium and titanium alloys. The corrosion-inhibitingcoating 109 can be formed from a corrosion-inhibiting coatingcomposition 105 that includes a corrosion-inhibiting agent 101, such asa non-chromium-based corrosion inhibiting particle. Thecorrosion-inhibiting agent 101 may be incorporated with acorrosion-inhibiting coating composition 105 that includes a matrix 107,such as a resin, for example an epoxy (in the case of coatings for anairplane's interior), an olefin, such as polyurethane (in the case ofcoatings for an airplane's exterior), both the epoxy and the olefin (inthe case of multilayer coatings used for both internal and externalpurposes), and an epoxy or olefin and sol-gel coating system (in case ofcoating for an airplane's exterior). The matrix 107 may be athermoplastic polymer such as polyvinylbutyral.

Corrosion-inhibiting agent 101, as described above, may be thecorrosion-inhibiting particle 301 illustrated in FIG. 3.Corrosion-inhibiting particle 301 may be an organic or inorganiccompound that imparts corrosion resistance to a metal when at least aportion of it is dissolved. For example, the particle may include aninsoluble thiol or sulfide containing organic molecule. The particle mayinclude a core 303 formed of, for example, a corrosion inhibitor, suchas a water soluble corrosion inhibitor. To form the coating compositionthat includes the corrosion-responsive agent and the epoxy, as describedabove, the corrosion-responsive agent may be transported in a solvent.In the case that the corrosion-responsive agent described above, is acorrosion-inhibiting particle, the particle may be reactive. That is,the corrosion inhibitor of the corrosion-inhibiting particle's core maybe reactive. For example, if the corrosion inhibitor reacts undesirablyduring the formation of a cured coating, the corrosion-inhibitingproperties may be consumed and unable to provide protection againstcorrosion. Thus, the corrosion-inhibiting particle 301 may also includea protectant 305 disposed on at least a portion of a surface of thecore. In other words, the core 303 may include a corrosion inhibitor andthe protectant may be configured to reduce reaction between the core andan epoxy or olefin resin, for example, the epoxy or olefin resin matrixof corrosion-inhibiting coating composition 105. In an example, theprotectant may be configured to reduce cross-linking between the coreand the epoxy resin or the olefin resin matrix. The protectant may bewater-permeable so as to allow water to reach the core and dissolve thecorrosion-inhibitor to form a dissolved corrosion-inhibitor. Theprotectant may also be configured to allow for the diffusion ofdissolved corrosion-inhibitor through the protectant.

The core may have a size in a range from about 100 nm to about 5 μm, forexample, from about 100 nm to about 1 μm. As described further below,the core may be a micronized core. That is, core 303 may be attained byreducing the particle size of a crude particle, such as via micronizing.In an example, particle size may be reduced by air-milling of asynthesized or commercially purchased, crude non-chrome corrosioninhibitor. As used herein, the term “non-chrome” refers to materialsthat are chromium free, for example, they may not include chromium (VI).

The corrosion inhibitor may be a polydisulfide, such as amercaptan-terminated polysulfide of dimercaptothiadiazole (DMcT).Micronizing or reducing crude particle size, for example, by milling thecrude corrosion inhibitor, may be performed to enrich reactive groups,such as the thiol functional groups of the mercaptan-terminated chainsof the polydisulfide corrosion inhibitor, on a surface of a particlecore. The polydisulfide may be represented by formula I:

where n is 1 or 2, and polymers thereof.

The protectant 305 may be disposed on at least a portion of the surfaceof core 303. For example, the protectant 305 may encapsulate the core303 forming a shell surrounding the core. The protectant 305 may becovalently bonded to the core. For example, as described further below,the protectant may be covalently bonded to a thiol functional groupextending from the core, such as extending from the core's surface.Accordingly, the protectant formed on a surface of the core may beviewed as a core-shell corrosion-inhibiting particle.

In one example, the core is configured with its surface enriched withthe thiol functional groups of the thiol-terminated corrosion-inhibitor.Enrichment may be performed by reducing the particle size, such as viamicronizing crude corrosion-inhibitor material. A reactive-group of aprotectant-forming material, such as the epoxy ring of an epoxideprotectant-forming material, may react with the thiol group, thuscovalently bonding the protectant-forming material to the thiol groupsto form the shell. Accordingly, the shell may be covalently bonded tothe core.

The micronized core may be introduced directly to a corrosion-inhibitingcoating composition. Thus, thiol groups enriched on the surface of themicronized core may react with a component of a corrosion-inhibitingcoating composition, for example, an epoxy of the coating composition,without forming a discrete shell over the core. This may preserve otherportions of corrosion-inhibitor in the core, such as internalcorrosion-inhibitor in the core that does not extend to the surface ofthe core. Thus, corrosion-inhibitor not extending to the surface of thecore and located within the core may remain free to performcorrosion-inhibiting function even after the coating composition iscured.

The micronized core may be introduced directly to a corrosion-inhibitingcoating composition that includes a protectant-forming material portion,such as a protectant-forming fluid, and a matrix portion. Theprotectant-forming fluid and a matrix portion of the composition may bethe same type of material. Thus, the protectant-forming material mayinclude a first portion and the matrix material may be considered asecond portion of the protectant-forming material. Micronized coreparticles with enriched surfaces comprising functional groups, such asthiol functional groups as described above, may be placed in contactwith the protectant-forming fluid. At least the first portion of theprotectant-forming material may react with the surface functional groupsof the micronized particles to form a protectant on at least a surfaceof the core, thereby forming core-shell corrosion-inhibiting particles.The second portion of the protectant-forming material may not react withthe functional groups on the micronized cores, and may remain as thematrix material for the coating formed from the coating composition inwhich the core-shell particles are dispersed.

The protectant disposed on a surface of the core may be capable ofreacting with the matrix material of the coating composition, such as amatrix 107, which may include a cross-linking agent. Accordingly,protectant 305, such as a shell covalently bonded to the core, may beviewed as a sacrificial component. For example, protectant 305 may reactwith the surrounding environment during processing to preserve thecorrosion-inhibitor in the core 303, and reduces reaction between thecorrosion inhibitor and the surrounding environment of cross-linkablematerial in the matrix. The micronized core of the particles describedherein may be functionalized by neutralization of the corrosioninhibitor. This neutralization step provides for improved adhesion of acoating that includes the particles described herein to a substrate, forexample, a metal substrate, on which it is applied.

The surface of the core may be enriched, for example, via micronizing acrude corrosion inhibiting particle, with at least one functional groupof the corrosion inhibitor. The functional group may have the formula Xor —R—X, where X is selected from, for example, a mercapto (i.e., —SH orthiol) and may be linked to the corrosion inhibitor of the core by R,which may be an alkyl chain, such as a lower alkyl (C₁-C₆) chain, analkyl ether group or an alkyl amine group. Accordingly, the functionalgroup may have the formula —(CH₂)_(n)—SH, where n may be an integerselected from the range that includes from 0 to 6, for example, from 1to 6, such as from 0 to 3. As used herein, the term “alkyl” may refer toa straight or branched chain saturated cyclic (e.g., cycloalkyl) oracyclic hydrocarbon group of from 1 to 12 carbons. Alkyl groups mayinclude C₁-C₈, C₁-C₆, C₁-C₈, C₂-C₇, C₃-C₁₂, and C₃-C₆ alkyl. Specificexamples include methyl, ethyl, 1-propyl, 2-propyl, 2-methyl-1-propyl,1-butyl, 2-butyl, and the like. Alkyl groups, used in any contextherein, may optionally be substituted with halogen, amino or sulfylgroups, or may include one or more heteroatoms in the alkyl chain, suchas oxygen (an ether) or nitrogen (an amine).

FIG. 4 includes a flow-chart 400 that illustrates a method for forming acorrosion inhibiting particle, such as corrosion-inhibiting particle301, and for forming a corrosion-inhibiting composition, such as acorrosion-inhibiting composition 105. Generally, in such a method forpreparing a corrosion inhibiting particle, a core comprising a corrosioninhibitor, such as core 303, is formed. Additionally, a protectant, suchas protectant 305 is formed on the surface of the core. The protectantmay be formed by covalently or ionically bonding at least one of areactive component of a protectant-forming composition to the corrosioninhibitor.

At 401, a crude corrosion inhibitor particle is provided. The crudecorrosion inhibitor particle may be synthesized according to knownmethods such as those described for “unprotected” corrosion inhibitorparticles as in Comparative Example 4 and Comparative Example 5described below, which are based on synthesis procedures disclosed inU.S. Pat. No. 4,599,425 granted on Jul. 8, 1986 and U.S. Pat. No.4,107,059 granted on Aug. 15, 1978, respectively. Preparation of acorrosion inhibitor may include precipitation of an insoluble species,such as by dissolving a compound in an organic solvent and thenprecipitating the corrosion inhibitor out of solution by adding thedissolved compound into a non-solvent. For example, a compound such asbis-DMcT may be dissolved in an organic solvent such as THF, and thedissolved bis-DMcT may be added to water to precipitate a crudecorrosion inhibitor particle. Alternatively, crude corrosion inhibitorparticle may be derived from VANLUBE® 829 (available from VanderbiltChemicals, LLC, Norwalk, Conn.), or INHIBICOR® 1000 (available fromWayne Pigment Corporation, Milwaukee, Wis.), or a combination of both.An organic structure of a representative crude corrosion inhibitor isshown in FIG. 5A as organic structure 303′, and includesmercaptan-terminated chains 304′.

Returning to FIG. 4, the crude corrosion-inhibitor particle may befiltration dried at 403. At 403, particle core, such as core 303 isformed by micronizing the crude corrosion inhibitor particle to a size,such as predetermined size, of about 0.1 μm to about 5 μm, for example,0.1 μm to about 5 μm using a suitable micronization process. Forexample, crude corrosion-inhibiting particle can be processed via airmill or other micronizer. While not limited to any particular theory, itis believed that micronizing the crude corrosion-inhibitor exposesfunctional groups of the corrosion-inhibitor, such asmercaptan-terminated chains 304′, thereby enriching a surface of thecore 303 with functional group 304 as shown in FIG. 5B. Optionally,because micronizing the particles exposes functional groups of thecorrosion-inhibitor, in some cases, micronizing results in particleshaving acidic character (i.e., lower pH than crude, unmicronizedparticles of larger size). Therefore, after or during micronizing, thecorrosion-inhibiting particles may be neutralized such that surfacecharges provided by the exposed groups (for example newly exposed —SHgroups, wherein S has a negative charge and H has a positive charge),are neutralized. In one example, the neutralization may be achieved byexposing the particles to a base, such as NaOH or KOH, during or aftermicronization of the particles. A similar result may be achieved bycoating the particles (i.e., covalently bonding the particles), therebyforming a chemically neutral shell that protects the core from reactingwith a resin or sol-gel in which they are disposed when formulating acorrosion-inhibiting coating. In other words, such neutralization toform a chemically neutral shell protects the free-thiol groups describedbelow.

Returning to FIG. 4, uniform ones of the micronized cores having apredetermined size in the range of about 0.1 μm to about 5 μm, forexample, 0.1 μm to about 1 μm may be selected for further processing.For example, at 407 a protectant may be formed via coating and/orfunctionalizing a protectant material to a surface of the cores. To coatand/or functionalize a surface of the core, the micronized core may beintroduced into a fluidizer in which a coating material sprayer providesa protectant-forming composition that includes, for example, an epoxy.An organic structure 305′ representative of an epoxy is shown in FIG.5C.

In an example, the functional group 304 of the corrosion-inhibitor ofcore 303 may react with a reactive component of a protectant-formingcomposition, such as an epoxy ring, to form the corrosion-inhibitingparticle that includes a core 303 with a protectant disposed on thecore. That is, in a fluidizer, a fluidized bed may be formed thatcontains the micronized core and the protectant-forming composition,such as an epoxy, which can react with a surface group, such as an —SH(i.e., thiol) group of the corrosion inhibitor. The protectant may,therefore, functionalize to a surface of the core. In other words, thegroups exposed on the surface of the core as a result of micronizing thecrude corrosion inhibitor may react with a surroundingprotectant-forming material, such as at least one of an epoxy resin. Inthe case of a core comprising a mercaptan-terminated polysulfide ofdimercaptothiadiazole corrosion-inhibitor, a reactive component of theprotectant-forming composition reacts with the “free” —SH (thiol) on theparticle surface, via, for example, formation of a covalent bondtherewith, and forms a protectant that may surround the core. In anexample, the protectant covalently bonded to the core forms a shell thatsurrounds the core. In an example, the protectant encapsulates the core.Alternatively, the micronized cores may be immersed in an organicsolution of epoxy followed by solvent removal.

As discussed above with respect to FIGS. 2A-2B, at 409 thecorrosion-inhibiting particles that include a core and a protectantdisposed on the core may be incorporated into a coating composition,such as a paint/coating formulation as at 409 in FIG. 4. The coatingformulation may then be applied to a substrate followed by air-dryingand/or UV curing to form a corrosion-inhibiting coating. Such a coatingmay be permeable to allow water to diffuse therein. Additionally, suchwater may diffuse across the protectant, such as a protectant that iswater-permeable, in order to reach particle's core. Upon reaching theparticle's core, the water may dissolve the corrosion-inhibitor whichcan then subsequently diffuse out and reach a coating defect site andabsorb to exposed underlying metal substrate, thereby inhibitingcorrosion of the substrate. It is noted that the corrosion-inhibitorcore of the corrosion-inhibiting particle may be coated with acontrolled release protectant. For example, the protectant may be awater soluble coating or a pH sensitive coating such aspoly(meth)acryltates used in pharmaceutical applications, for example,EUDRAGIT® acrylic polymers available from Evonik Industries, AG, Essen,Germany. Thus, in the case of a water-soluble protectant, uponcontacting water, the water-soluble protectant dissolves therebyreleasing the corrosion-inhibitor from the core. In the case of a pHsensitive protectant, the protectant may dissolve or becomes permeablein acid or basic aqueous environments encountered in corrosionprocesses, thereby releasing the corrosion inhibitor of the core.

As shown in FIG. 5B, core 303 may be enriched with functional group 304,such as a thiol-terminated end group of the corrosion inhibitor. Thethiol-terminated end group may react with a material such as acomponent, for example organic structure 305′, of a protectant-formingcomposition, to at least partially cover the surface of core 303, as inFIG. 5D. Such coverage may protect the core's corrosion inhibitor, forexample, when the particle is incorporated in a matrix of a coatingcomposition that includes a cross-linkable resin. Exemplarycross-linkable resins in such coating compositions include aliphaticamine-cured epoxies, polyamide epoxy, polyamine adducts with epoxy,kerimine epoxy coatings, aromatic amine-cured epoxies, silicone modifiedepoxy resins, epoxy phenolic coatings, epoxy urethane coatings, coal tarepoxies, oil-modified polyurethanes, moisture cured polyurethanes,blocked urethanes, two component polyurethanes, aliphatic isocyanatecuring polyurethanes, polyvinyl acetals and the like, ionomers,fluorinated olefin resins, mixtures of such resins, aqueous basic oracidic dispersions of such resins, or aqueous emulsions of such resins,and the like. Methods for preparing these polymers are known or thepolymeric material is available commercially. It should be understoodthat various modifications to the polymers can be made such as providingit in the form of a copolymer.

The corrosion-inhibiting coating may be formed from a composition formedof a mixture of at least two components, such as an epoxy (component A)and a hardener (component B). Accordingly, component A, component B, oreach of components A and B may include the corrosion inhibitingparticles comprising the core and protectant disposed on at least asurface of the core as described above. Alternatively, the coatingcomposition may additionally include a separate source of the corrosioninhibiting particles (component C) which may be mixed with either one oreach of component A and component B so long as the coating compositionincludes the corrosion inhibiting particles described above, and acarrier, for example, at least one of an uncured epoxy resin and anuncured olefin resin.

The formulation that is used in forming the corrosion-inhibiting coatingmay be applied to a substrate by an appropriate coating method, such asdip coating, spin coating, and spray coating.

In addition to the corrosion-inhibiting particle and cross-linkableresin, coating formulations can contain other materials. For example,any plasticizer, colorant, curing catalyst, residual monomer,surfactant, or any other material that adds useful properties to thecoating, or at least does not reduce the functionality of the coating,can be included in the coating in amounts that are known to those ofskill in the art of polymer compounding.

It is believed that the present methods can be used to prevent or reducecorrosion for any corrodible metal. The methods and compositions areparticularly useful on steel and aluminum alloys, and more particularlyon aluminum/copper alloys. For example, the aluminum/copper alloys arethose that comprise at least 1% by weight copper, such asaluminum/copper alloys that contain at least 4% by weight copper, forexample, copper-containing aluminum alloys AA2024 and AA7075.

EXAMPLES Example 1 Preparation of Crude Corrosion Inhibiting Particlesfrom VANLUBE® 829

Crude corrosion inhibitor having a composition that includes a structurerepresented by formula (II) was derived from VANLUBE®829 available fromVanderbilt Chemicals, LLC.

Example 2 Particle Size Reduction of VANLUBE® Corrosion Inhibitor,Dispersion of Reduced-Particle-Size VANLUBE® 829 Corrosion Inhibitorinto Solvent Based Sherwin Williams Polyurethane Primer CM0480,Formation of Protectant Via Reaction of Corrosion Inhibitor withPolyurethane, and Formation of Corrosion-Inhibiting Coating for Use on E41 Sample Series Substrates

Particle size reduction to enrich the particles' surfaces withfunctional groups and dispersion of dry VANLUBE® 829 in Sherwin WilliamsJetFlex Reducer/thinner CM0110845 was carried out by combining 1.50 gVANLUBE® 829 with 4.0 mls CM0110845 reducer with 5.0 mls of 2 mm glassbeads in a 60 ml plastic bottle and subjecting it to 20 minutes ofmixing at 750 rpm on a Thinky planetary mixer. The 60 ml plastic bottlewas initially wrapped with a sufficient amount of ⅛″ thick AP/Armaflexinsulation tape to prevent it from spinning inside the holder of theThinky mixer. An additional 4.0 mls of CM0110845 reducer was added tothe mix bottle to decrease the paste-like viscosity of theVANLUBE®/reducer mixture following the 20 minute mixing period.

A 14.00 g portion of Sherwin Williams polyurethane primer was combinedwith with 2.00 g Sherwin Williams primer catalyst CM0120930 and 4.0 mlsCM0110485 reducer in a 60 ml plastic bottle and mixed for 20 minutes at750 rpm on a Thinky planetary mixer for initial mixing of the primerbinder components. Following this initial mixing of the primer binder,the mixture of dispersed VANLUBE® 829 in CM0110485 reducer was added tothe primer binder mixture. Core-shell corrosion-inhibiting particleswere formed via reaction of surface functional groups enriched on thesurface of the reduced-particle-size VANLUBE® 829 corrosion inhibitorwith the polyurethane. Two additional 1.0 ml portions of CM0110485reducer was added to the VANLUBE® 829 dispersion bottle to help rinseout glass beads and VANLUBE® residues on the inside walls of thecontainer and then added to the primer. The combined primer and VANLUBE®829 inhibitor components were then given a final 20 minute mix at 750rpm on the Thinky mixer before straining it through a paper paint filterto remove the glass beads. The remaining portions of the polyurethaneprimer that did not react to form a protectant on the corrosioninhibitor formed a matrix in which the core-shell corrosion-inhibitingparticles were dispersed and the dispersion was collected in an airbrushreservoir prior to spray application to substrates.

Example 3 Forming Corrosion-Inhibiting Composition and Coating

The corrosion-inhibiting particle of Example 2 was introduced into apaint (i.e., coating) formulation. The coating formulation was appliedto a substrate and air dried or UV cured.

Example 4 Use of a Disulfide/Dithiol Compound to Increase CorrosionResistance of Aluminum and its Alloys

A 1% solution of 5,5-dithiobis-(1,3,4-thiadiazole-2(3H)-thione) was madeup of VANLUBE® 829 in deionized water. This mixture was processed on apaint shaker using glass beads to help incorporate the VANLUBE® into thewater. A high speed shear mixer or a centrifugal planetary mixer wouldhave worked as well. The VANLUBE® did not dissolve, but a portion wasreduced to nano-sized particles which stayed in suspension.

2024-T3 aluminum panels (3″×6″×0.032″) were used as test specimens.Three of these panels were chromium conversion coated to use ascontrols. Three panels were put through an aluminum cleaning processingline (solvent wipe, alkaline clean and deoxidized) prior to immersion inthe 1% solution. Immersion time was 5 minutes at room temperature. Thesepanels were then rinsed. Three panels were wet abraded with Scotch-Brite7447 pads, rinsed and allowed to dry. The 1% solution was then sprayapplied to the panels. The panels were kept wet with the solution for 2minutes at room temperature. These panels were then allowed to air dry.Three panels were solvent wiped only to use as control panels.

All the panels were then placed into neutral salt spray per ASTM B-117for testing. After 4 hours of exposure the chromium panels wereunaffected. The panels which had been abraded, however, performed betterthan the immersed and rinsed panels or the bare unprocessed panels.

The use of a disulfide/dithiol compound (even in water), while not aseffective as hexavalent chrome, improved the corrosion resistance ofaluminum and its alloys.

COMPARATIVE EXAMPLES Comparative Example 1 Preparation ofCorrosion-Inhibiting Coating Formulation that Includes UnprotectedCorrosion-Inhibiting Particles

Waterborne epoxy coating formulations containing varying amounts ofunprotected VANLUBE® corrosion inhibitor and/or pigments and fillermaterials were prepared and tested for their ability to serve ascorrosion resistant coatings on bare 2024 T3 aluminum substrates.Formulation were based on one listed in U.S. Pat. No. 8,114,206, grantedon Feb. 14, 2012, which is incorporated by reference herein in itsentirety. The binder for theses coatings consisted of EPI-REZ 6520-WH-53resin and EPIKURE 6870-W-53 obtained from Momentive Specialty Chemicals.VANLUBE® 829 from Vanderbilt Chemicals, LLC was the principal corrosioninhibitor used in these coating, although a zinc oxide treated versionof VANLUBE® 829 was also evaluated in one formulation. Additionalpigments and fillers used in the formulations included Kronos 2310 TiO2,Alfa Aesar barium metaborate, Azco BC-1-20 wet ground mica and N-200ceramic microspheres from Zeeospheres.

Comparative Example 2 Preparation of Corrosion-Inhibiting Coatings

Corrosion-inhibiting coatings were prepared from the coatingformulations of Comparative Example 1. For example, some samples wereprepared by spin coating 3″×3″×0.040″ thick bare 2024 T3 aluminumsubstrates. Surface preparation for these early samples consistedsolvent wiping to remove panel marking inks and hand washing with anALCONOX® detergent solution until a water break-free surface wasobtained. No de-oxidation step or further processing of the substrateswith either ALODINE® (available from Henkel Corporation of Rocky Hilly,Conn., or BOE-GEL® (available from The Boeing Company, Chicago, Ill.)surface treatments was performed in order to limit potential corrosionrate influences strictly to formulation components. Coating samples forothers of the formulations were prepared by spray application using anIwata Eclipse airbrush, using 20 PSI triggered air pressure.Approximately 25 mls of coating solution was prepared for eachformulation and was sufficient to coat nine 3″×3″ panels using the Iwataairbrush, with coating solution left over. The resulting samples wereallowed to air dry overnight and were then given accelerated cures at160 F for at least 2 hours before performing any tests.

Comparative Example 3 Characterization of Corrosion-Inhibiting CoatingsFormed from Formulations Containing Unprotected VANLUBE® 829Corrosion-Inhibitor

Physical properties of the water borne epoxy coating formulationscontaining a mixture of VANLUBE® 829, pigment and filler package atloadings levels as low as 15 PVC were poor, even those with low pigmentloading level. Coating samples from formulations with 26 to 45 PVCloading levels were noticeably chalky when touched. During BSS 7225 Type1, Class 3 dry tape adhesion tests, the tape readily pulled particlesfrom the outer surface of the samples, while the rest of the scribedcoating appeared to remain adhered to the panel surface. Althoughinitially appearing to past the adhesion test, these coating were veryeasy to damage or remove from the substrate via scratching. Waterresistance of such coatings was also poor.

Initially, the poor physical characteristics of the coatings wereattributed to unknown oil absorption characteristics of the VANLUBE® 829material that may have putting much higher wetting demands on the epoxybinder than had initially been thought. To test this assumption,coatings with progressively lower VANLUBE® 829 and pigment loadinglevels were prepared and tested. Reasonable physical properties werefirst obtained when VANLUBE® 829 was used alone as the sole pigment orfiller material at loading levels of 5.9 PVC and 10 PVC. However, theaddition of approximately 5 PVC of the pigment and filler materials tothe 10 PVC VANLUBE® 829 coating formulation, weak coatings with poorstrength and weak water resistance were produced.

The dramatic deterioration of coating physical properties at relativelylow overall inhibitor and pigment loading levels indicated that VANLUBE®829 might be reacting with either the epoxy resin component or cureagent of the waterborne coating system. The possible reaction ofVANLUBE® 829 thiol groups with either the epoxy ring of the binder resinor amine groups of the cure agent may be a potential consequence of theaddition of this corrosion inhibitor to epoxy coating systems.

To further investigate whether VANLUBE® 829 was interfering with thecure of the epoxy coating, vials containing amounts of the epoxy resinand cure agent normally used to prepare the waterborne coating sampleswere prepared and mixed, with and without the amount of VANLUBE® 829used to prepare a 10 PVC coating. After 24 hours of aging in the sealedvials, the epoxy binder without VANLUBE® 829 had stiffened noticeablyand developed a dryer texture. In contrast, the consistency of the epoxybinder that had been mixed with VANLUBE® 829 appeared to be unchanged,indicating possible interference by the added corrosion inhibitor withthe cure of the coating. When this test was repeated using zinc-VANLUBE®instead of VANLUBE® 829, a very slight increase in coating viscosity wasnoticed after 24 hours. This result was interpreted as an indicationthat the less reactive zinc-VANLUBE® had a somewhat less detrimentaleffect on the cure of the epoxy coating system than the originalVANLUBE® 829 material.

Comparative Example 4 Synthesis of bis-[2,5-dithio-1,3,4-thiadiazole](BDTD)

Synthesis of bis-[2,5-dithio-1,3,4-thiadiazole] was performed accordingto the following synthesis scheme:

A corresponding procedure, similar to that disclosed in U.S. Pat. No.4,599,425, was followed: 15 grams of DMCT (0.1 mole), FW=150.22, in theform of a powder was suspended in 200 ml of water at 0° C. Whilevigorously stirring the suspension, 14 grams of 30% hydrogen peroxidesolution (corresponding to 0.1 mole) was added dropwise (using theperistaltic pump) at a slow rate such that the reaction temperature didnot exceed 50° C. 1 hour after the addition of the peroxide, the BTDTwas filtered off, washed three times with DI water and dried at 50° C.for 12 hours.

Comparative Example 5 Synthesis of poly(2,5-dithio-1,3,4-thiadiazole)(PDTD)

Synthesis of poly(2,5-dithio-1,3,4-thiadiazole) was performed accordingto the following synthesis scheme:

A corresponding synthesis procedure, similar to that disclosed in U.S.Pat. No. 4,107,059, was followed: 22 grams (0.1 mole) of dipotassium1,3,4-thiadiazole-2,5-dithiolate KDMCT (0.1 mole) was dissolved in 200ml of water at 20° C. 25.1 grams ammonium persulfate was dissolved in120 ml water. While vigorously stirring the KDMCT solution, thepersulfate solution was added dropwise with a peristaltic pump over aperiod of 45 minutes. The solution was stirred an additional hour(solids formed during this period). The resulting PDTD product waswashed 4× with 200 ml water. The solids were transferred to a Waringblender, dispersed in 200 ml water and acidified with 0.1 M HCl to bringthe pH to 2.0. The product was washed again with water (6×250 ml) anddried in a vacuum desiccator.

Comparative Example 6 Micronization and Neutralization of INHIBICOR®1000

The particle size of INHIBICOR®1000 (available from WPC Technologies,Milwaukee, Wis.) was decreased from 3.49 μm (FIG. 6A) to 2.50 μm (FIG.6B) using a Micronizer jet mill from Sturtevant. As shown in FIGS. 7A,7B and 7C, non-micronized (as-is), micronized and INHIBICOR®1000particles, were formulated in high strength AC-131 (4% w/vINHIBICOR®1000 in 6% v/v of (Si+Zr) in AC-131) and sprayed evenly onbare Al 2024 panels. The solubility of the INHIBICOR®1000 increased inthe resin matrix as a result of the micronization, as observed forpanels in FIGS. 7A-7B. However “river-like” patterns were observed onthe panel (b) (FIG. 7B) due to poor adhesion of the coating. The pooradhesion of the coating was attributed to a drop in pH observed betweennon-micronized particles (6.35 pH) and micronized particles (5.63 pH).While not limited to any particular theory, it is believed that as aresult of micronization, the newly exposed surfaces of micronizedparticles are enriched with reactive groups, such as —SH groups. As aresult, it is believed that more negatively charged and positivelycharged atoms of the reactive groups (e.g., more negatively charged Satoms and positively charged H atoms on the surface of the micronizedparticles) provide for a lowering of the pH in an aqueous mixture ascompared to non-micronized particles also in an aqueous mixture. Thus,to improve the adhesion of the coating, the micronized INHIBICOR®1000particles were neutralized by exposing the micronized particles to abase. In an example, the micronized particles were placed in water andthe neutralizing was performed by titrating to neutral pH (e.g., pH of7) with 1M NaOH. A coating prepared from the micronized and neutralizedcorrosion inhibiting particles was prepared under similar conditions asthose coatings described for FIGS. 7A and 7B, and the results of forminga coating on a test substrate, the coating comprising micronizedparticles that have been neutralized by exposing them to a base, isshown in FIG. 7C. A comparison of FIG. 7B and 7C shows that the “riverlike” patterns are no longer present as a result of the neutralizingstep, showing that neutralization improved the adhesion of to the Al2024 panel.

The results of Linear Sweep Voltammetry (LSV) (FIG. 8) andChronoamperometry (FIG. 9) show effects of micronizing and neutralizingINHIBICOR 1000® particles as tested for the coatings as described abovefor FIGS. 7A-7C. As shown in FIG. 8, micronized corrosion inhibitingparticles as described herein (B) also improved the inhibition ofoxygen-reduction-reaction (ORR) at the surface of a Cu rotating diskrelative to coatings that included as-is, unmicronized INHIBICOR 1000®particles (A). As shown by the results in FIG. 3 results, a largeramount of the inhibitor leached out of the coating as was visible by thedecreasing ORR current with time. Meanwhile, neutralizing the micronizedparticles (C) slightly decreased the coating's ability to inhibit ORR.When the panel was coated heavily (D) with the same solution (C) (2 minspray time as compared to ˜30 sec) leaching of the inhibitor out of thecoating was negligible in a 2 hr time-frame.

While the present teachings have been illustrated with respect to one ormore implementations, alterations and/or modifications may be made tothe illustrated examples without departing from the spirit and scope ofthe appended claims. For example, it will be appreciated that while theprocess is described as a series of acts or events, the presentteachings are not limited by the ordering of such acts or events. Someacts may occur in different orders and/or concurrently with other actsor events apart from those described herein. Also, not all processstages may be required to implement a methodology in accordance with oneor more aspects or descriptions of the present teachings. It will beappreciated that structural components and/or processing stages may beadded or existing structural components and/or processing stages may beremoved or modified. Further, one or more of the acts depicted hereinmay be carried out in one or more separate acts and/or phases.Furthermore, to the extent that the terms “including,” “includes,”“having,” “has,” “with,” or variants thereof are used in either thedetailed description and the claims, such terms are intended to beinclusive in a manner similar to the term “comprising.” The term “atleast one of” is used to mean one or more of the listed items may beselected. Further, in the discussion and claims herein, the term “on”used with respect to two materials, one “on” the other, means at leastsome contact between the materials, while “over” means the materials arein proximity, but possibly with one or more additional interveningmaterials such that contact is possible but not required. Neither “on”nor “over” implies any directionality as used herein. The term “about”indicates that the value listed may be somewhat altered, as long as thealteration does not result in nonconformance of the process or structureto the illustrated descriptions. Finally, “exemplary” indicates thedescription is used as an example, rather than implying that it is anideal. Other implementations of the present teachings will be apparentto those skilled in the art from consideration of the specification andpractice of the disclosure herein. It is intended that the specificationand examples be considered as exemplary only, with a true scope andspirit of the present teachings being indicated by the following claims.

Other implementations will be apparent to those skilled in the art fromconsideration of the specification and practice of what is describedherein. It is intended that the specification and examples be consideredas exemplary only, with a true scope and spirit of the implementationsbeing indicated by the following claims.

What is claimed is:
 1. A chemically reactive, non-chromecorrosion-inhibiting particle comprising: a micronized core comprised ofa thiol-containing corrosion inhibitor, wherein the micronized corecomprises a particle size in a range of about 100 nm to about 5 μm. 2.The particle of claim 1, wherein the core comprises a chemicallyneutralized surface.
 3. The particle of claim 1, wherein the corrosioninhibitor is water soluble.
 4. The particle of claim 1, wherein thecorrosion inhibitor comprises a polydisulfide.
 5. The particle of claim1, wherein the corrosion inhibitor comprises a mercaptan-terminatedpolysulfide of dimercaptothiadiazole.
 6. The particle of claim 1,wherein the corrosion inhibitor comprises a mercaptan-terminatedcorrosion-inhibitor.
 7. The particle of claim 1, further comprising aprotectant disposed on at least a portion of a surface of the core andcovalently bonded to a thiol group of the corrosion inhibitor.
 8. Theparticle of claim 7, wherein the protectant is water-permeable, andwherein dissolved corrosion-inhibitor can diffuse through theprotectant.
 9. The particle of claim 7, wherein the protectantencapsulates the core.
 10. The particle of claim 7, wherein theprotectant is configured as a shell surrounding the core.
 11. Acorrosion-inhibiting composition, comprising the corrosion-inhibitingparticle of claim 7 and a carrier, wherein the carrier comprises atleast one selected from the group consisting of an epoxy resin and anolefin resin, and the protectant reduces cross-linking between the coreand the epoxy resin or the olefin resin.
 12. A method for preparing achemically reactive, non-chrome corrosion-inhibiting particle, themethod comprising: providing a thiol-containing, chemically reactivecorrosion-inhibitor; micronizing the corrosion inhibitor to have aparticle size in a range of about 100 nm to about 5 μm.
 13. The methodof claim 12, wherein the corrosion-inhibitor comprises amercaptan-terminated polysulfide.
 14. The method of claim 12, furthercomprising exposing the micronized corrosion inhibitor to a base. 15.The method of claim 14, wherein the base is selected from NaOH or KOH.16. The method of claim 13, further comprising forming a protectant onat least a portion of the surface of the core by covalently bonding atleast one of a reactive component of a protectant-forming composition toa thiol group of the corrosion-inhibitor.
 17. The method of claim 16,wherein the protectant-forming composition comprises an epoxy resin. 18.An article, comprising: a metal substrate,; and a corrosion-inhibitingcoating disposed on the substrate and comprising a chemically reactive,non-chrome corrosion-inhibitor particle incorporated in an epoxy or anolefin, wherein the corrosion-inhibitor particle comprises: a corecomprising a chemically reactive corrosion inhibitor.
 19. The article ofclaim 18, wherein the corrosion-inhibitor is water soluble.
 20. Thearticle of claim 18, wherein the corrosion-inhibitor comprises apolydisulfide.
 21. The article of claim 18, wherein thecorrosion-inhibitor comprises a mercaptan-terminated polysulfide ofdimercaptothiadiazole.
 22. The article of claim 18, wherein thecorrosion-inhibitor particle further comprises a protectant disposed onat least a portion of a surface of the core, the protectant covalentlybonded to a thiol group of the corrosion inhibitor and configured toreduce reaction between the core and the epoxy or the olefin.
 23. Thearticle of claim 22, wherein the protectant is water-permeable, andwherein dissolved corrosion-inhibitor can diffuse through theprotectant.
 24. The article of claim 22, wherein the protectant isconfigured as a shell surrounding the core.
 25. The article of claim 22,wherein the metal comprises aluminum, aluminum alloy, steel, magnesium,magnesium alloy, copper, copper alloy, tin, tin alloy, nickel alloy,titanium, titanium alloys, or combinations thereof.
 26. A method ofpreparing a non-chrome corrosion inhibitor coating compositioncomprising a disulfide/dithiol compound, the method comprising: forminga mixture comprising a 1% solution of5,5-dithiobis-(1,3,4-thiadiazole-2(3H)-thione) in water; and agitatingthe mixture to form a suspension comprising nano-sized particlescomprising the 5,5-dithiobis-(1,3,4-thiadiazole-2(3H)-thione), whereinthe nano-sized particles stay in suspension.
 27. The method of claim 26,further comprising incorporating glass beads in the mixture, and whereinagitating comprises shaking the mixture in a paint shaker.
 28. Themethod of claim 26, further comprising incorporating glass beads in themixture, and wherein the agitating comprises mixing the mixture with theglass beads in a high speed shear mixer.
 29. The method of claim 26,further comprising incorporating glass beads in the mixture, and whereinthe agitating comprises mixing the mixture with the glass beads in acentrifugal planetary mixer.
 30. The method of claim 26, wherein the5,5-dithiobis-(1,3,4-thiadiazole-2(3H)-thione) does not dissolve in themixture.